Mattress



FIG. 1 is a front, top perspective view of an embodiment of a mattress showing my new design;

FIG. 2 is a left side view thereof, the right side being a mirror image thereof; and,

FIG. 3 is a front view thereof, the rear view being a mirror image thereof.

The broken lines are environmental and form no part of the claimed design. 

The ornamental design for a mattress, as shown and described. 